Hue and saturation control circuitry requiring single coupling capacitor

ABSTRACT

A signal-processing circuit comprises a first gate circuit, a chrominance signal amplifier, a hue control circuit, means for reproducing a composite color signal, an AC coupling capacitor, and a second gate circuit. The first gate circuit receives a composite color signal consisting of chrominance signals and burst signals which are arranged alternately and then extracts the chrominance signals and burst signals from the composite color signal. The extracted chrominance signal is amplified by the chrominance signal amplifier, while the phase of the extracted burst signal is controlled by the hue control circuit. The outputs of the chrominance signal amplifier and the hue control circuit are added by said reproducing means, thereby reproducing a composite color signal. The AC coupling capacitor is coupled to the output of said means. The second gate circuit extracts from the output of the AC coupling capacitor chrominance signals and burst signals.

This invention relates to an analog signal-processing integrated circuit which comprises various circuits formed on one chip and wherein the number of necessary terminal pins is reduced.

Generally, the more circuits are used to constitute an analog IC, the more transistors should be connected in cascade. The more transistors are connected in cascade, the more is varied the DC component of an analog signal. Thus, it is necessary to cut the DC transmission path at a point and to apply only the AC component of the analog signal to the succeeding stages. To apply the AC component of the analog signal alone, a capacitor of a large capacity should be used. But it is difficult to incorporate such a capacitor into an integrated circuit. Thus a capacitor of a large capacity should be connected to the external terminal pins of the analog IC. In consequence, the number of necessary terminal pins of the analog IC increased inevitably.

With reference to FIGS. 1 and 2 a conventional chrominance signal-processing circuit, an example of an analog IC used in TV sets, will be described. As shown in FIG. 1, the conventional chrominance signal-processing circuit comprises a composite color signal amplifier 1, a gate circuit 2, a hue control circuit 3, a chrominance signal amplifier 4, a demodulator 5 and a phase detector 6. The gate circuit 2 extracts a burst signal e_(b) and a chrominance signal e_(c) from an amplified chrominance signal (e_(b) +e_(c)) from the amplifier 1 in response to a gate pulse generated in synchronism with the burst signal. The burst signal e_(b) is supplied to the hue control circuit 3, while the chrominance signal e_(c) is supplied to the chrominance signal amplifier 4, which controls the gain of the chrominance signal e_(c). The phase detector 6 is to control a subcarrier wave oscillator (not shown) or to generate a control signal for automatic color control or color killer control.

The chrominance signal amplifier 4 and the hue control circuit 3 have output terminals P₁ and P₃, respectively. Similarly, the demodulator 5 and the phase detector 6 have input terminals P₂ and P₄, respectively. A capacitor C₁ is connected between the terminals P₁ and P₂, and another capacitor C₂ between the terminals P₃ and P₄. Both capacitors act as AC coupling elements.

Each of demodulator 5 and phase detector 6 usually includes such differential amplifiers of double balanced type as illustrated in FIG. 2. More specifically, transistors Q₁ and Q₂ constitute a differential amplifier, transistors Q₃ and Q₄ another differential amplifier, and transistors Q₅ and Q₆ still another differential amplifier. The emitters of the transistors Q₃ and Q₄ are connected to the collector of the transistor Q₁, the emitters of the transistors Q₅ and Q₆ to the collector of the transistor Q₂, and the emitters of the transistors Q₁ and Q₂ to a current source I_(o). The collectors of the transistors Q₃ and Q₅ are connected to a power source V_(cc) through a load resistor R₁. The collectors of the transistors Q₄ and Q₆ are connected also to the power source V_(cc). To one end of the resistor R₁ there is connected an output terminal P₁₁.

A burst signal e_(b) or a chrominance signal e_(c) is supplied to the base terminal P₇ of the transistor Q₁ and/or the base terminal P₈ of the transistor Q₂. Subcarrier waves are supplied to the common base terminal P₉ of the transistors Q₃ and Q₆ and/or the common base terminal P₁₀ of the transistors Q₄ and Q₅. If a circuit in the preceding stage is connected to the base terminals P₇ and P₈, the voltage across the terminals P₇ and P₈, i.e. DC bias on the differential amplifier constituted by the transistors Q₁ and Q₂, will be lowered. As a result, the maximum amplitude of an input signal will be limited, or the voltage at the output terminal P₁₁ will vary. Consequently, the demodulator 5 may change the color of the background on the TV screen, and the phase detector 6 may eventually vary the frequency of the subcarrier waves from the subcarrier wave oscillator (not shown).

To avoid the variation of the voltage across the terminals P₇ and P₈, an AC coupling capacitor is connected to the terminal P₇ or P₈. The conventional chrominance signal-processing circuit shown in FIG. 1, which controls chrominance signals (first signals) and burst signals (second signals) alternately transmitted in time-share fashion, requires two AC coupling capacitors, i.e. capacitors C₁ and C₂. In case the signal-processing circuit is used in a TV set, the capacitors C₁ and C₂ should have such a large capacity as would provide a sufficiently small impedance to the TV signal frequency, e.g. 3.58 MHz. With such a large capacity, the capacitors C₁ and C₂ can hardly be made into an integrated circuit. For this reason they should be arranged outside the signal-processing circuit which is an IC. In conventional circuit the signal-processing circuit should therefore be provided with four external terminal pins P₁ to P₄. A large number of pins is one of the factors which make it difficult to incorporate various circuits into an integrated circuit. If four terminal pins P₁ to P₄ are used merely to allow the use of two AC coupling capacitors, it means that the pins P₁ to P₄ are not used effectively.

The object of this invention is to provide a signal-processing circuit which comprises various circuits performing different functions and wherein the number of necessary terminal pins is reduced thereby to make it easier to incorporate the various circuits into an integrated circuit.

According to one aspect of this invention there is provided a signal-processing circuit comprising signal-separating means for separating and extracting a first signal and a second signal from a multiplex signal; a gain control circuit for controlling the gain of the first signal from said signal-separating means; a phase control circuit for controlling the phase of the second signal from said signal-separating means; means for synthesizing the outputs of said gain control circuit and said phase control circuit to form a time-shared type signal; and an AC coupling capacitor for supplying the time-shared type signal from said signal-synthesizing means to a circuit in the next stage.

This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram of a conventional signal-processing circuit;

FIG. 2 is a circuit diagram of one example of a phase detecting circuit shown in FIG. 1;

FIG. 3 shows a block diagram of a signal-processing circuit according to one embodiment of this invention;

FIG. 4 is a concrete circuit diagram of the signal-processing circuit shown in FIG. 3;

FIG. 5 is a circuit diagram of a color killer circuit;

FIG. 6 is a circuit diagram showing another embodiment of this invention; and

FIG. 7 shows a vector diagram for explaining the operation of the circuit shown in FIG. 6.

As shown in FIG. 3, an embodiment of the signal-processing circuit according to this invention comprises a composite color signal amplifier 1, a first gate circuit 2, a hue control circuit 3, a second chrominance signal amplifier 4, a demodulator 5, a phase detector 6 and a second gate circuit 7. The first gate circuit 2 separates a chrominance signal e_(c) and a burst signal e_(b) when a gate pulse is applied to the first gate circuit 2. The hue control circuit 3 and the chrominance signal amplifier 4 have a common output terminal P₅, and the second gate circuit 7 has an input terminal P₆. Between the terminals P₅ and P₆ there is connected an AC coupling capacitor C₃.

Unlike in the conventional signal-processing circuit of FIG. 1, the outputs of the hue control circuit 3 and second chrominance circuit 4 are synthesized at the output terminal P₅ to form a sum signal (e_(c) +e_(b)), which is supplied to the second gate circuit 7 through the capacitor C₃. That is, the sum signal consisting of a chrominance signal e_(c) and a burst signal e_(b) passes through the capacitor C₃, and the chrominance signal e_(c) separated again from the burst signal e_(b) by the second gate circuit 7. The chrominance signal e_(c) is then supplied to the demodulator 5, and the burst signal e_(b) to the phase detector 6. Instead, to the capacitor C₃ there may be connected two gate circuits, one for extracting the chrominance signal from the sum signal and the other for extracting the burst signal from the sum signal.

As shown in FIG. 3, the signal-processing circuit requires but a single AC coupling capacitor in order to supply a chrominance signal e_(c) and a burst signal e_(b), which have undergone a specific control, to the demodulator 5 and the phase detector 6, respectively. Provided with only one AC coupling capacitor, the signal-processing circuit requires only two terminal pins. Indeed the second gate circuit 7 is an additional element, and it changes little the DC component of the sum signal. Thus the operation of the demodulator 5 or the phase detector 6 is hardly affected by the variation of the DC component. Further, the hue control may be effected by subcarrier wave signals instead of burst signals e_(b) from the first gate circuit 2. The hue control can be carried out even if the second chrominance signal amplifier 4 is not provided.

A concrete circuit diagram of one embodiment of this invention is shown in FIG. 4, which is not provided with a hue control circuit corresponding to the hue control circuit amplifier 3 of the circuit shown in FIG. 3. This embodiment comprises a composite color signal amplifier 1, a first gate circuit 2, a chrominance signal amplifier 4, an AC coupling capacitor C₃, a demodulator 5 and a phase detector 6. The demodulator 5 denotes only one demodulated axis, and the phase detector 6 actuates a voltage-controlled oscillator VCO.

In the signal-processing circuit of FIG. 4, the gate circuit 2 is constituted by a by-pass capacitor C_(B), transistors Q₇ and Q₈, resistors R₂ to R₄, a differential amplifier of double balanced type comprised of transistors Q₉ to Q₁₂, and a base terminal P₁₂ connected to the bases of the transistors Q₉ and Q₁₂. The gate circuit 2 separates a burst signal e_(b) from a composite color signal (e_(b) +e_(c)) when a gate pulse is applied to the terminal P₁₂. The phase detector 6 is constituted by transistors Q₁₆ to Q₂₀ and Q₂₂ to Q₂₅, resistors R₁₀ to R₁₂ and capacitors C₅ and C₆. The chrominance signal amplifier 4 is constituted by transistors Q₁₃ to Q₁₅, resistors R₅ to R₈ and a variable resistor RV₁. The demodulator 5 is constituted by transistors Q₂₆ to Q₃₅ and resistors R₁₃ to R₁₇. The gate circuit 2, chrominance signal amplifier circuit 4, demodulator 5 and phase detector 6 are of well-known type, and their constructions are not described here in detail.

A processed composite signal (e_(b) +e_(c)) from the chrominance signal amplifier 1 is applied to the base of the transistor Q₇ of the gate circuit 2. But the base of the transistor Q₈ is DC-biased by the by-pass capacitor C_(B). The collectors of the transistors Q₁₀ and Q₁₂ are connected to the junction between the emitters of the transistors Q₁₃ and Q₁₄ of the chrominance signal amplifier, and the collectors of the transistors Q₉ and Q₁₁ to the base of transistor Q₁₅ of the chrominance signal amplifier 4.

When a gate pulse is applied to the terminal P₁₂, the transistors Q₉ and Q₁₂ of the gate circuit 2 are rendered conductive. The transistors Q₉ and Q₁₂ remain conductive for a burst period, during which time a burst signal e_(b) is extracted from the composite color signal (e_(b) +e_(c)) and supplied to the base of the transistor Q₁₅ through the transistor Q₉. During a chrominance signal period the transistors Q₁₀ and Q₁₁ remain conductive and a chrominance signal e_(c) is supplied to the emitters of the transistors Q₁₃ and Q₁₄ through the transistor Q₁₀. The chrominance signal e_(c) is supplied further to the base of the transistor Q₁₅ which is connected to the resistor R₈.

The ratio of the current flowing through the transistor Q₁₄ and the current flowing through the transistor Q₁₃ is controlled by the variable resistor VR₁. The chrominance signal e_(c) which has passed through the transistor Q₁₄ is supplied to the transistor Q₁₅. In this way the color gain of the chrominance signal e_(c) is controlled.

The transistor Q₁₅ and the resistor R₉ of the chrominance signal amplifier 4 form a emitter follower. The chrominance signal e_(c) which has undergone amplitude control and the burst signal e_(b) which has undergone no amplitude control appear alternately in time-share fashion at the output terminal P₅ of the chrominance signal amplifier 4. These signal e_(c) and e_(b) are supplied through the AC coupling capacitor C₃ to the phase detector 6 and the demodulator 5. The sum signal (e_(c) +e_(b)) is applied to the base of the transistor Q₁₇ of the phase detector 6 and to the base of the transistor Q₂₇ of the demodulator 5.

In the phase detector 6, the transistors Q₁₇ to Q₂₀ constitute a differential amplifier. The transistors Q₁₈ and Q₁₉ have their bases connected mutually, their emitters connected to the emitter of the transistor Q₁₇ and the emitter of the transistor Q₂₀, respectively, and their collectors connected to the collector of the transistor Q₁₇ and the collector of the transistor Q₂₀, respectively. The bases of the transistors Q₁₈ and Q₁₉ are connected to a terminal P₁₃. When a negative gate pulse is applied to the terminal P₁₃, the transistors Q₁₈ and Q₁₉ become inconductive and the transistors Q₁₇ and Q₂₀ become conductive, whereby the phase detector 6 comes into operation. Namely, the phase detector 6 operates during the burst signal period and remains inoperative during the other period.

In the demodulator 5, the transistors Q₂₇ to Q₃₀ constitute a differential amplifier. The transistors Q₂₈ and Q₂₉ have their bases connected mutually, their emitters connected to the emitter of the transistor Q₂₇ and the emitter of the transistor Q₃₀, respectively, and their collectors connected to the collector of the transistor Q₂₇ and the collector of the transistor Q₃₀, respectively. The bases of the transistors Q₂₈ and Q₂₉ are connected to a terminal P₁₄. To the terminal P₁₄ a positive gate pulse is applied. When a positive gate pulse synchronized with the negative gate pulse is applied to the terminal P₁₄, the transistors Q₂₈ and Q₂₉ become conductive and the transistors Q₂₇ and Q₃₀ become nonconductive. As a result, a burst signal e_(b) is shut off. While no burst signal e_(b) is applied to the transistor Q₂₇, the transistors Q₂₇ and Q₃₀ remains conductive. That is, during the chrominance signal period these transistors are conductive, thereby to demodulate the chrominance signal e_(c). Thus, the demodulator 5 operates during the chrominance signal period, while the phase detector 6 operates during the burst signal period.

The gate pulse used in the conventional signal-processing circuit as shown in FIGS. 1 and 2 is a flyback pulse or a horizontal synchronizing signal. A horizontal synchronizing signal is preferred because it has a stable phase relationship with a burst signal e_(b). In a weak electric field, however, a horizontal synchronizing signal contains noise and in some cases it fails to perform a perfect gating operation. As a result, a chrominance signal e_(c) may erroneously enter the hue control circuit 3 during the chrominance signal period. If this happens, color killer control should be carried out in the demodulator 5 or the phase detector 6.

FIG. 5 shows another embodiment of this invention which differs from the signal-processing circuit of FIG. 4 only in that a color killer control circuit 8 is connected between demodulator 5 and a phase detector 6. The color killer control circuit 8 is constituted by transistors Q₃₆ to Q₃₈ and resistors R₁₈ to R₂₁. The output of the phase detector 6 is coupled to the base of the PNP transistor Q₃₈, the emitter of which is connected to a power source V_(cc) through the resistor R₂₁. The collector of the transistor Q₃₈ is grounded through the resistor R₂₀ and connected to the base of the transistor Q₃₇. The emitter of the transistor Q₃₇ is grounded, and the collector thereof is connected to the emitter of the transistor Q₃₆ via the resistor R₁₉. The collector of the transistor Q₃₆ is connected to a voltage source V_(B7) through the resistor R₁₈ and further to the terminal P₁₄ of the demodulator 5. The base of the transistor Q₃₆ is connected to a terminal P₁₆, to which a negative gate pulse is applied.

In a sufficient electric field, the transistor Q₃₈ is conductive, and a current flows through the resistor R₂₀. Thus the transistor Q₃₇ is saturated, and the resistor R₁₉ is equivalently grounded. As a result, the transistor Q₃₆ comes into operation to supply a positive gate pulse to the terminal P₁₄ of the demodulator 5. In a weak electric field, the transistor Q₃₈ is nonconductive, and no current flows through the resistor R₂₀. The transistor Q₃₇ is therefore turned off, and then the transistor Q₃₆ is turned off, too, whereby the positive gate pulse is not supplied to the terminal P₁₄ of the demodulator 5. Eventually the potential at the terminal P₁₄ reaches the value at the voltage source V_(B7), and the transistors Q₂₈ and Q₂₉ of the demodulator 5 remain conductive thereafter, whereby color killer operation is carried out.

FIG. 6 shows a further embodiment of this invention, which differs from the signal-processing circuits shown in FIG. 4 in that it has further a hue control circuit. The circuit of FIG. 6 is divided into two parts by a dotted line. The right part is identical with the combination of the gate circuit 2 and the chrominance signal amplifier 4 of the signal-processing circuit shown in FIG. 4, except that the collectors of transistors Q₉ and Q₁₁ are connected to a power source V_(cc).

In the left part of the circuit of FIG. 6, the output of a composite color signal amplifier 1 which amplifies both a burst signal e_(b) and a chrominance signal e_(c) is coupled to the bases of transistors Q₃₉ and Q₄₆ through a resistor R₂₂. The base of the transistor Q₃₉ is grounded through a capacitor C₄. Thus, the resistor R₂₂ and the capacitor C₄ constitute a phase delay circuit. The output of the composite color signal amplifier 1 is supplied also to the base of a transistor Q₄₂ and further to the base of a transistor Q₇. The emitter of the transistor Q₃₉ is connected to the emitter of a transistor Q₄₀. The emitters of these transistors Q₃₉ and Q₄₀ are connected to a current source I_(o1) through a resistor R₂₃. The other end of the current source I_(o1) is grounded. The emitters of a pair of transistors Q₄₁ and Q₄₂ are mutually connected and are connected to the current source I_(o1) through a resistor R₂₄. The emitters of another pair of transistors Q₄₃ and Q₄₄ are mutually connected and are coupled to a current source I_(o2) through a resistor R₂₅. Similarly, the emitters of another pair of transistors Q₄₅ and Q₄₆ are mutually connected and are coupled to the current source I_(o2) through a resistor R₂₆.

The base of the transistor Q₄₃ is connected to the base of a transistor Q₈, while the bases of the transistors Q₄₀, Q₄₁, Q₄₄ and Q₄₅ are connected to a terminal P₁₇, to which a gate pulse is applied. The collectors of the transistors Q₃₉ and Q₄₀ are mutually connected to the junction between the emitters of a pair of transistors Q₄₇ and Q₄₈. The collectors of the transistors Q₄₁ and Q₄₂ are mutually connected and are coupled to the power source V_(cc) l through a resistor R₃₀ and also to a terminal P₁₈. The collectors of the transistors Q₄₃ and Q₄₄ are mutually connected and are coupled to the junction between the emitters of a pair of transistors Q₄₉ and Q₅₀. The collectors of the transistors Q₄₅ and Q₄₆ are mutually connected and are coupled to the power source V_(cc).

The bases of the transistors Q₄₇ and Q₅₀ are mutually connected and coupled to a voltage source V_(B2) through a resistor R₂₉ and to a DC control variable resistor VR₂ through a resistor R₂₇. The bases of the transistors Q₄₈ and Q₄₉ are mutually connected and coupled to the voltage source V_(B2) through a resistor R₂₈. The collectors of the transistors Q₄₇ and Q₄₉ are mutually connected and coupled to the power source V_(cc), while the collectors of the transistors Q₄₈ and Q₅₀ are mutually connected and coupled to the base of a transistor Q₁₅.

It will be described how hue control is carried out by the circuit of FIG. 6, with reference to FIG. 7.

Suppose the output signal of the composite color signal amplifier 1 is vector a as shown in FIG. 7 and applied to the bases of the transistors Q₄₂ and Q₇. If the phase of the output signal is delayed by, for example, 45° by the phase delay circuit constituted by the resistor R₂₂ and the capacitor C₄, vector a will be converted into such vector b as illustrated in FIG. 7.

When a gate pulse is applied to the terminal P₁₇, the transistors Q₄₀, Q₄₁, Q₄₄ and Q₄₅ are rendered inconductive, while the transistors Q₃₉ and Q₄₂ start operating as a differential amplifier and the transistors Q₄₃ and Q₄₆ start operating as a differential amplifier. If a difference between vectors a and b (=a-b), as shown in FIG. 7, vector c appears at the collector of the transistor Q₃₉, and vector b appears at the collector of the transistor Q₄₃. Let vector a be the reference phase, here. Then, vector c is regarded as having a phase of +45°, and vector b as having a phase of -45°. Thus, |b|=|c|. In the differential amplifier of double balanced type constituted by the transistors Q₄₇ to Q₅₀ the amplitude ratio between vectors b and c is controlled by the variable resistor VR₂. Further, vectors b and c are synthesized into a signal, which is applied to the base of the transistor Q₁₅. The phase of this signal may thus range from -45° to +45° with respect to vector a. A burst signal with a controlled phase and a chrominance signal having its amplitude controlled by transistor Q₁₄ are synthesized at the base of the transistor Q₁₅ into a signal. The signal thus obtained is supplied from the emitter of the transistor Q₁₅ to the circuit in the next stage through an AC coupling capacitor C₃.

As mentioned above, in the signal-processing circuit according to this invention the number of the necessary AC coupling capacitors which serve to reduce the offset of DC coupling among the various circuits. Thus the number of the terminal pins of the signal-processing circuit is reduced proportionally. The signal-processing circuit is therefore made into an integral circuit more easily than otherwise. In addition, since the number of AC coupling capacitors is reduced, the signal-processing circuit can be manufactured at a lower cost. 

What is claimed is
 1. A composite color signal-processing circuit for processing a time-shared composite color signal including burst and chrominance signals at distinct time periods comprising:a vector signal generating circuit having an input coupled to said composite signal for generating first and second vector signals having different phases with respect to each other, said vector signal being generated during said burst signal period; a vector signal synthesizing means coupled to said vector signal generating circuit for controlling the relative absolute values of said first and second vector signals and for synthesizing said first and second controlled vector signals; a gain control circuit coupled to said composite color signal for extracting and controlling the gain of a chrominance signal from said composite color signal in response to a gate pulse; a common load coupled to the outputs of said vector signal synthesizing means and to said gain control circuit for combining their respective outputs; an AC coupling capacitor coupled to said common load for delivering an AC component of said combined outputs; a first phase detector coupled to said coupling capacitor for responding to said burst signal period in response to the gate pulse; and a second phase detector coupled to said AC coupling capacitor for responding to a chrominance signal in response to said gate pulse.
 2. A composite color signal-processing circuit according to claim 1 further including means for adapting an output of said first phase detector responsive to said burst signal period as an automatic phase control signal in response to the appearance of said gate pulse.
 3. A composite color signal-processing circuit according to claim 1 further including means for adapting an output of said first phase detector responding to said burst signal period as a color killer signal in response to the appearance of said gate pulse.
 4. A composite color signal-processing circuit according to any one of claims 1, 2, 3 wherein said vector signal generating circuit comprises:an input terminal to which a first vector signal is supplied; a phase shifter coupled to said input terminal for producing a second vector signal; a difference vector signal generator for producing a difference vector signal from said first and second vector signals in response to said gate pulse during said burst signal period; and a gate circuit for delivering said second vector signal from said phase shifter in response to said gate pulse during said burst signal period. 